Using historical records of droughts and current climate trends, scientists have created a new climate model for precipitation in the American Southwest. Their analysis puts the odds of a decade-long drought at 80 percent before the year 2100. In some areas, the probability is as high as 90 percent.
The researchers arrived at these probabilities by first combing paleoclimate data for evidence of past droughts. Reconstructions from the 1150s shows the Southwest experienced a nearly 25-year period of below-average rainfall, and a ten-year period when the Colorado River was at about 85 percent of its normal flow. In the twentieth century, the worst droughts in the U.S. took place during the 1930s (the “Dust Bowl” era) and the 1950s. Historically, the Southwest has averaged at least one nearly ten-year drought per century.
This data was then applied to current climate change models for the twenty-first century and used in a thousand Monte Carlo simulations. These simulations create a probability distribution by substituting a range of values for factors with inherent uncertainty.
The researchers found that their new models forecast a much higher probability of extreme drought than previous estimates.
As the authors state in their report, “state-of-the-art climate model projections suggest the risk of a decade-scale megadrought in the coming century is less than 50%; our analysis suggests that the risk is at least 80%, and may be higher than 90% in certain areas. The likelihood of longer lived events (> 35 years) is between 20% and 50%, and the risk of an unprecedented 50 year megadrought is non-negligible under the most severe warming scenario (5-10%).”
Using this model, not only is a ten-year drought in the next 85 years a high possibility, there is also a potentially 50/50 chance that the Southwest will experience a 35 year drought or longer.
The authors further state that these numbers are actually conservative estimates, as their model only accounts for decreased precipitation, not rising temperatures caused by global warming.
Their report, “Assessing the risk of persistent drought using climate model simulations and paleoclimate data,” has been published in the Journal of Climate.